Ja. Duffy et al., PHASE-TRANSITIONS OF CO2 CONFINED IN NANOMETER PORES AS REVEALED BY POSITRONIUM ANNIHILATION, Journal of physics. Condensed matter, 7(50), 1995, pp. 713-717
The results of a comprehensive positronium annihilation study of the p
hase behaviour of carbon dioxide in porous Vycor glass are presented.
Isobaric measurements of the 3 gamma:2 gamma annihilation ratio show t
hat on cooling, the gas-liquid phase boundary is raised by similar to
5 K while the liquid-solid transition is depressed by similar to 12 K
relative to the bulk. The resulting phase diagram suggests the existen
ce of a 'triple point' of the confined fluid at a temperature similar
to 10 K and a pressure similar to 2 bar below the bulk triple point.